Metadata basically means data about data. It tells about what, when, why, who, where, which, and how of data. In Talend, metadata has the entire information about the data which is present in Talend studio. The metadata option is present inside the Repository pane of Talend Open Studio.
Various sources like DB Connections, different kind of files, LDAP, Azure, Salesforce, Web Services FTP, Hadoop Cluster and many more options are present under Talend Metadata.
The main use of metadata in Talend Open Studio is that you can use these data sources in several jobs just by a simple drag and drop from the Metadata in repository panel.